Field of the Invention
The present invention relates to a polarization system.
Description of the Background Art
Photolithography is one of the central methods of semiconductor and microsystem technology for the production of integrated circuits and further products. Here, via exposure optics, a light source, for instance a laser source, exposes a mask, the pattern of which is imaged with the aid of projection optics onto a semiconductor wafer coated with photoresist. The resolution capacity, that is to say the capacity of the optical system to image the smallest structures in the photoresist, is determined substantially by the light wavelength used and the capability of the system to intercept sufficient orders of diffraction of the mask. It may be described approximately by:CD=k1*(λ/NA).
Here, CD is the critical dimension, which means the smallest line width that can be imaged (often also designated by the English terms minimum feature size or critical dimension), k1 is a factor dependent on the imaging and resist system, λ the wavelength of the light used and NA the numerical aperture of the last lens before the wafer.
In addition to the development of exposure technology and the use of smaller and smaller wavelengths down to the low UV range (including improving the numerical aperture), numerous further techniques for improving the process window by means of the reduction in the k1 value have been developed and introduced. In addition to improvements in the photoresists, these are primarily what are known as resolution-improving techniques. These include techniques for optimizing the exposure, such as oblique illumination (English off-axis illumination, OAI) or the exposure with polarized light.
Systems for producing polarized light are sufficiently well known from the prior art. For example, these can be cemented systems, in which crystals of various orientation directions are joined to one another. However, such systems cannot be used in the UV range, since the short-wave radiation would damage or even destroy the joining material. Also known are substrates with vapor-deposited layers, by means of which the light is broken down into a component transmitted the substrate and polarized and a component reflected on the layer and polarized. The transmitted and polarized component often used in the prior art is, however, transmitted with high losses at short wavelengths, so that use in the UV range is likewise possible only with very great difficulty.